1. Field of the Invention
Aspects of the present invention relate to a voltage converter, and more particularly, to a method and apparatus to control a voltage conversion mode of a voltage converter, such as a direct current to direct current (DC-DC) converter.
2. Description of the Related Art
In general, a voltage converter is a circuit which converts an input voltage to an output voltage that is different from that of the input voltage. FIG. 1 is a view showing an example of a direct current to direct current (DC-DC) converter, which is one kind of a voltage converter. Referring to FIG. 1, a DC input voltage supplied from a voltage source 110 is converted by a voltage converter 100 (a DC-DC converter) to a DC output voltage different from the input voltage and which is supplied to a load 120. The DC-DC converter is used in a mobile device that uses a battery as a voltage source or in various other devices.
In general, a voltage converter is classified into a DC-DC converter to convert a DC voltage into a DC voltage, an alternating current to alternating current (AC-AC) converter to convert an AC voltage into an AC voltage, a DC-AC converter to convert a DC voltage into an AC voltage, and an AC-DC converter to convert an AC voltage into a DC voltage. In addition, the voltage converter is classified into a switching converter and a linear converter. The switching converter controls an input voltage according to a supply period of a switching operation to generate an output voltage. In general, the switching converter is often used for a load which uses high power.
The switching converter may be distinguished between a pulse width modulation (PWM) converter or a pulse frequency modulation (PFM) converter. The PWM converter performs a switching operation every predetermined period in synchronization with a clock signal oscillating at a predetermined frequency. The PFM converter changes a switching period according to a power load. The linear converter attenuates an input voltage by a predetermined voltage to generate an output voltage having a desired magnitude. The linear converter uses a low drop out (LDO) method or the like, and is generally effective if used for the load which uses low power.
The voltage converter generally is most efficient if used with a specific input and a specific load, and accordingly, when the load decreases, a switching loss increases, and cause a decrease in a power efficiency. Therefore, a voltage conversion efficiency cannot be maximized according to changes of magnitudes in the input voltage, the output voltage, and the load, and a problem arise in that a usage time of a mobile device cannot be maximized.